America is drawing up plans for a "bloody nose" military attack on North Korea to stop its nuclear weapons programme.

The White House has "dramatically" stepped up preparation for a military solution in recent months amid fears diplomacy is not working, well-placed sources said.

One option is destroying a launch site before it is used by the regime for a new missile test.

Stockpiles of weapons could also be targeted.

The hope is that military force would show North Korean leader Kim Jong-un that America is "serious" about stopping further nuclear development and trigger negotiations.

Three sources - two former US officials familiar with current thinking and a third figure in the administration - confirmed military options were being worked up.

"The Pentagon is trying to find options that would allow them to punch the North Koreans in the nose, get their attention and show that we're serious," said one former US security official briefed on policy.

President Donald Trump's decision to bomb a Syrian government airfield earlier this year to defend America's "red line" on chemical weapons use is seen as a blueprint.

Details emerged after reporters talked to around a dozen current and former officials in America and Britain about policy towards North Korea. The conversations show that the Trump administration is more willing to consider military options to end the conflict than widely assumed.

It can be revealed that senior British diplomats fear America has already begun a "step by step" military build-up in the region that could escalate.

Alastair Morgan, the UK ambassador to North Korea, visited Washington DC for behind-closed-doors talks about forcing the regime to the negotiating table last month.

The UK is also urging south-east Asian and African countries to expel some North Korean diplomats amid fears they are secretly financing the regime.